Hydrocarbons (oil, condensate and gas) are typically produced from wells that are drilled into the formations containing them. For a variety of reasons, such as inherently low permeability of the reservoirs or damage to the formation caused by drilling and completion of the well, the flow of hydrocarbons into the well may be low. In this case, the well can be stimulated, using a variety of techniques, including hydraulic fracturing.
During the drilling of a wellbore, various fluids may be used for multiple functions. The fluids may be circulated through a drill pipe and a drill bit into the wellbore, and then may subsequently flow upward through the wellbore to the surface. During the circulation, the a fluid may act to remove drill cuttings from the bottom of the hole to the surface, to suspend cuttings and weighting material when circulation is interrupted, to control subsurface pressures, to maintain the integrity of the wellbore until the well section is cased and cemented, to isolate fluids from the formation by providing a sufficient hydrostatic pressure to prevent the ingress of the fluids onto the wellbore, to cool or lubricate the drill string and drill bit, and/or to maximize a penetration rate.
In many well treatments, a fluid may be injected into the well under pressure. If some or all of the fluid leaks of the wellbore, a fluid loss occurs. In certain treatments where fluid is intended to be returned to the surface, such as drilling, some or all of the fluid may not return due to a fluid loss. This is termed “lost circulation.” There are numerous products and techniques, such as using polymer pills and cement plugs, to cure lost circulation. One approach is to add a lost circulation material (LCM) into the drilling fluid and/or into the cement or polymer system. LCM systems often contain fibers.
In hydraulic fracturing in particular, a fluid is injected into the formation to initiate and propagate a fracture. Then, a second fluid is injected to keep the fracture open after the pressure is released. During hydraulic fracturing, one or more of the fluids will be pumped into the wellbore until the downhole pressure exceeds the fracture gradient of the rock.
In hydraulic fracturing of horizontal wells and multi-layered formations, diverting techniques may be used to enable fracturing redirection between different zones. Known diverting methods include mechanical isolation devices such as packers, as well as well bore plugs, setting bridge plugs, pumping ball sealers, pumping slurred benzoic acid flakes and removable or degradable particulates.
When diversion using diverting materials is performed downhole, the diversion is generally based upon bridging of some particles of the diverting material and forming a plug by accumulating the rest of the particles at the formed bridge. However, when removable materials are used in a typical treatment diversion, the bridging ability of the diverting slurry may be reduced because of dilution with a wellbore fluid. Further, poor stability of the plug formed from various diverting materials is another concern during such a diversion procedure.
Plugging or diverting a downhole feature with solid diverting materials such as degradable materials may be achieved when the diverting agent is at a high loading (e.g., at a high concentration), such as from about 20 lbs/1000 gal to about 1000 lbs/1000 gal, or from about 40 lbs/1000 gal to about 750 lbs/1000 gal) in order to form temporary plugs or bridges. The solid diverting materials material may also be used at concentrations at least 4.8 g/L (40 lbs/1,000 gal), at least 6 g/L (50 lbs/1,000 gal), or at least 7.2 g/L (60 lbs/1,000 gal). High loading of the solid diverting materials may lead to multiple particle blocking of porous media. However, achieving a high loading of solid diverting materials within a stream of treatment fluid is challenging.
The ability to add a solid into a treatment fluid in a continuous manner with traditional solid feeders so as to be functional in a particular operation downhole (such as a diverting and/or plugging operation) is difficult because the solid feeders are limited in their feeding rates. This is of particular concern for diversion in hydraulic fracturing treatments, for which treatment fluid is to be injected at a high rate, often exceeding 50 barrels (bbl)/min, and where the rate of addition of the solid should be substantial enough to create a stream of high loading solid material.
Plugging a downhole feature may be utilized to address lost circulation. which is defined as the partial or total loss of drilling fluids into the formation; it can take place while drilling, tripping into the hole, running casing or cementing. One approach to remediate to loss circulation consists in sealing fractures with various particulate-based plugging materials.
To aid in a diversion and/or plugging treatment, the solid material to be used may be a degradable material, and such material may be in the form of manufactured shapes such as flakes, fibers and particles. Methods for diversion using degradable materials is described in U.S. Pat. No. 7,380,600, U.S. Pat. No. 8,167,043, U.S. Pat. No. 7,565,929, and U.S. Patent Application Publication No. 2008/0210423, each of which is hereby incorporated by reference in its entirety. However, such known materials may not reliably operate efficiently, may cause congestion when passing through fracturing pumps and the like, and may necessitate substantial user intervention.